1. Field of the Invention
The present invention relates to an air-cooled electronic apparatus.
2. Description of the Related Art
Recently, in an electronic apparatus such as a high-end server or a super computer, attempts have been made to form a processor from a high density integrated circuit module to obtain higher performance. Further, attempts have been made to form a system from a plurality of processors so that higher performance is achieved by parallel processing.
The integrated circuit module forming the processor has one or more highly integrated chips, such as a CMOS chip, mounted at high density and operates at high speed. The amount of heat generated from each chip and the integrated circuit module is very large and therefore it is important to effectively and economically remove the generated heat.
When the system is constructed from a plurality of processors, processors are generally mounted in such a way that a plurality of integrated circuit modules are mounted to a single circuit board for the purpose of wiring each of the processors to the others. In such a case, for example, soldering is used for mounting the integrated circuit module to the circuit board. According to this circuit board structure, the electronic apparatus is shipped from a factory either in the condition that all the integrated circuit modules to be mounted are attached or in the condition that the integrated circuit modules required by the customer at the time of delivery are attached. Therefore, the customer must handle the circuit board carrying the integrated circuit modules as a unit when, for example, trouble occurs to necessitate replacement of parts, which causes the maintenance cost to increase because the price of a unit is high.
Also, when it is necessary to increase or decrease the number of processors in the system in response to the customer's demand, the circuit board structure must be returned to the factory as a whole, which is a troublesome work. To eliminate such inconveniences, the integrated circuit modules forming the processors are preferably mounted to the circuit board via connectors so that the integrated circuit module is attachable to, and detachable from, the circuit board by the customer. This is convenient because it is sufficient to stock the integrated circuit modules or others as maintenance parts. Also, the integrated circuit module or others handled in such a manner is favorably as small as possible in size. Recently, a technology for realizing such a demand has been strongly desired.
In the prior art electronic apparatus having a cooling system, integrated circuit modules are mounted to a circuit board via connectors to construct a system or a subsystem of an electronic equipment. A heat sink is attached to the integrated circuit module so that the heat sink having a number of heat transfer fins is disposed in a cooling air passageway when the integrated circuit module is mounted to the connector. Heat generated from the integrated circuit module is thus radiated from the heat sink.
As processors have achieved increasingly higher performance, heat generated from the integrated circuit modules has increased. Therefore, it is necessary to increase the cooling capacity as the generated heat increases. In the prior art air-cooling system, the cooling effect is satisfied if the speed of cooling air is in the range from 4 to 5 m/sec when the heat generating density is 3 W/cm.sup.2 or less, but it is very difficult to handle generated heat exceeding the above-mentioned value with an air-cooling system.
Therefore, a liquid-cooling system is employed in place of the air-cooling system, to increase the cooling capacity. In the liquid-cooling system, a cold plate through which cooling water is circulated is brought directly, or via a heat sink, into contact with the integrated circuit module to cool the latter. The liquid-cooling system, however, has a drawback in that this necessitates a cold plate and a mechanism for circulating cooling water, including a pump, piping, a heat exchanger or others, which is less economical than the air cooling system.
In the air-cooling system, the area of the heat transfer fins may be enlarged to lower thermal resistance of the heat sink to increase the cooling capacity. However, thermal resistance is not always lowered in proportion to the increase in the area of the heat transfer fins. As the area of the heat transfer fins increases, the size and the weight of the integrated circuit unit, including the integrated circuit module and the heat sink, become larger, which results in difficulty in handling, and necessitates a structural member other than the connector for supporting the weight of these members. Under such circumstances, it is required that the integrated circuit module be easily mounted to the circuit board and be more effectively and economically cooled.